Presently a wide variety of magnetic field sensors are already known. Of particular interest are magnetodiode sensors of the kind that employ a semiconductive element into which are injected hole and electron charge carriers from opposite ends. The semiconductive element is made inhomogeneous so that it includes at least two regions of very different recombination times for charge carriers therein. A magnetic field to be sensed is made to traverse the semiconductive element in a specific direction. In that direction, the resulting Lorentz force deflects the charge carriers initially injected into one of the two regions into the other of the two regions. Such deflection results in a change of the amount of current flowing between the two ends of the semiconductive element. The basic principles of magnetodiode sensors of this kind are described in a paper by Kataoka entitled "Recent Developments of Magnetoresistive Devices and Applications" in circular #182 of the Electromechanical Laboratory, Agency of Industrial Science and Technology, Tokyo, Japan, Dec. 1974.
The present invention relates to a magnetodiode type of magnetic sensor that is well adapted for use as a position sensor, particularly for automotive applications, although its application is not so limited.
In a magnetic field sensor of the kind described, sensitivity depends importantly on two parameters: (1) the mobilities of the charge carriers in the semiconductive material forming the magnetodiode, and (2) the recombination time T.sub.R. T.sub.R is the average time it takes for a charge carrier of one sign to recombine with a charge carrier of the opposite sign after injection of the charge carrier into the semiconductive material. Recombination occurs before the charge carrier reaches its charge collecting electrode. We do not know what specifically happens to the charge carriers when they recombine, but the result is a reduction in electrical current flow between complementary electrodes of the magnetodiode.
For high sensitivity to the effects of a magnetic field, the mobilities of the charge carrier should be high because the amount of deflection of the path of a charge carrier in the presence of a magnetic field normal to the path is proportional to the product of carrier mobility and magnetic field strength.
Also, for high sensitivity to the effects of a magnetic field, carrier recombination times should be long because the average distance a charge carrier will travel in a semiconductive material is proportional to the product of the recombination time and the drift velocity of the charge carrier.
In semiconductive materials readily available for use in sensors of the kind described, a semiconductive material such as silicon which is an indirect band-gap material, has a carrier recombination time that is attractively long. However, it has carrier mobilities that are relatively low. As indicated above, high mobilities are needed to obtain a magnetodiode having high sensitivity to a magnetic field. On the other hand, some compound semiconductors, such as GaAs, InAs, Bi.sub.1-X Sb.sub.X, and InSb, which are direct band-gap materials, have carrier mobilities that are attractively high. However, their carrier recombination times are normally undesirably short. Because the recombination times are short, these materials have not been as sensitive as would be liked. The present invention represents a new approach to overcome the above shortcomings of the normally short carrier recombination times in such, i.e., direct band-gap, compound semiconductors. This approach involves using these latter materials to form distinctive diode structures that exhibit considerably longer carrier recombination times than conventional diode structures.